All eddy current induction/detection devices are obviously governed by Lenz's reflective law. A permanent magnet floating above a superconductor (Meissner effect) illustrates a literal flux suspension system. Reciprocally, the hemispherical driving flux fringing from the polar coordinates sensor in Logue U.S. Pat. No. 5,909,118 that allowed several degrees of probe tilt, was the result of a flux suspension system provided by an annular air gap between the driving core and the pick-up core. Copending Logue et al. patent application Ser. No. 09/873,838 disclosed an integral driving/sensing pot-core half wherein the flux suspension system comprised connecting the poly-phase excitation windings in a series ring; thus providing a greater degree of differential redistribution of the H field in response to probe tilt. The present disclosure adds a high premeability ballast toroidal inductance in series with the x-y coordinates excitation turns, in effect a differential flux equalization means.
Remember diameterwise excitation of a toroidal core (x-y axes of permeability) is not a closed loop, therefore, high frequency response is good.
The mechanical equivalent is left to right differential linkage means and a longer stabilizer spring travel in an automobile suspension system.
Early Logue eddy current devices were called “polar coordinates” sensors e.g. Logue U.S. Pat. No. 5,939,880 comprising a pick-up core (pot-core half) and a driving core (poly-phase motor stator) i.e. a concentric arrangment being magnetically neutralized due to inherent orthogonality between driving and sensing axes of permeability. Logue et. al. U.S. Pat. No. 6,265,871 taught eddy current induction-detection by utilization of a rotating diametric dipole sensing hemisphere/s (see FIG. 1) fringing from the equatorial plane of a toroidal core 55xx. The term “polar coordinates sensor” is intended to convey more than planar geometry, by prior description i.e. “a hemispherical sensing pattern” (Logue U.S. Pat. No. 5,548,212) fringing diameter-wise from the equatorial plane of a high permeability toroidal core/s. Therefore, “polar coordinates” also includes varying degrees of Lenz latitude of eddy current depth within the workpiece. Obviously the reciprocal of polar coordinates is x-y coordinates. To avoid ambiguity, “polar coordinates sensor” will continue be the generic term used herein.